An agricultural harvester known as a “combine” is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating, and cleaning. A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing rotor. The threshing rotor rotates within a perforated housing, which may be in the form of adjustable concaves, and performs a threshing operation on the crop to remove the grain. Material other than grain (MOG) such as straw from the threshing section proceeds through a straw chopper and out the rear of the combine to more easily incorporate the remaining residue in subsequent tillage practices. Once the grain is threshed it falls through perforations in the concaves and is transported to a grain pan. From the grain pan the grain is cleaned using a cleaning system. The cleaning system includes a cleaning fan which blows air through oscillating sieves or shoes to discharge chaff and other debris toward the rear of the combine. The clean grain is then transported upwards via a clean grain elevator to a grain tank onboard the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, and an unloading system, e.g., an unloading auger, on the combine is actuated to transfer the grain into the vehicle.
The combine may additionally include a rethreshing process to recapture the “tailings”, i.e. the remaining grain and MOG mixture that is left over after the cleaning process. The tailings may include the grain that is still attached to the fragments of a head, as in barley, or it may include the kernels that are attached to the fragments of a cob, as in corn. Generally, the tailings are either rethreshed through the main threshing mechanism, such as a conventional cylinder, or processed through an additional threshing unit. Typically, after the cleaning process a tailings auger and/or conveyor is used to transport the tailings to one or both sides of the combine and back to the main threshing mechanism or additional threshing unit. After rethreshing, the tailings are returned to the cleaning system. If an additional threshing unit is used, the tailings may be returned to the cleaning system by impellers, blowers, and/or augers.
If the main threshing mechanism is used for rethreshing, the tailings may overload the main threshing mechanism and will inevitably cause excessive wear on the main threshing mechanism. If an additional, separate threshing mechanism is used for rethreshing, the load on the main threshing mechanism is lessened; however, the processing results are generally inferior compared to rethreshing the material through the main threshing mechanism. Additionally, an externally mounted additional threshing mechanism can be cumbersome and may occupy a large amount of space on the exterior of the combine.
What is needed in the art is an agricultural harvester that can efficiently and cost-effectively rethresh tailings.